4lO
I. Papadakis and G.A. Schultz
historical river flows on the basis of satellite information alone. In order to find out
how much satellite information is really required in order to meet the hydrological
goal, a sensitivity analysis has to be done by which the amount of satellite data to
be used can be optimized.
18.3 Application
In order to show, how the approach described in Sect. 18.2 functions in practice an
example will be presented.
Due to the fact that the approach discussed here is mainly meant for planning of
water management systems in countries of the developing world, it seems appropriate to give an example from the tropics. On the basis of an existing cooperation
between the Institute of Hydrology, Water Management and Environmental Techniques of the Ruhr-University Bochum and the Water Resources Research Unit,
CSIR, in Ghana, West Africa, the Tano river basin in Ghana was chosen.
IS.3.1 Study area and data used
The Tano river basin comprises a catchment area of about 16.000 km 2 , in which
daily records from 23 raingauges for the period of 1983-1984 are available. The
raingauge density is 1 gauge per 700 km 2 and their distribution over the catchment
is reasonably uniform. Additionally measured monthly runoff values and monthly
rainfall for the periods from 1969 - 1972, 1975 - 1976 and 0711984 - 0411985 are
also available. The observed daily rainfall data are accumulated in monthly values,
since for planning purposes of water management systems monthly data are usually adequate. The required monthly area precipitation is computed from the available point measurements with the aid of the reciprocal distance weighting method.
In West Africa, where the test catchment is located, rainfall intensity and distribution in space is dependent on the migration of the ITDZ (Inter Tropical Discontinuity Zone). The ITDZ is the front where two air masses of different origin and
characteristics converge (Tropical Continental Air Mass and Tropical Maritime
Air Mass). The migration of the ITDZ gives rise to two well-defined seasons (wet
and dry). The months July and August are dry although the ITDZ is farthest north
(wet season) which means that the atmospheric water vapour is high. This situation
is defmed as a climatic anomaly over West Africa. Especially for the Tano river
basin two main seasons are defined, namely the wet season in which the whole
catchment area under consideration is influenced only by maritime air masses
excluding the months July and August (short dry season) and the dry or relatively
dry season in which the catchment area is influenced mostly by continental air
masses (Ojo, 1977). Figure 18.5 shows the location of the catchment in a semi-arid
area in Ghana, West Africa.
I. Papadakis and G.A. Schultz
historical river flows on the basis of satellite information alone. In order to find out
how much satellite information is really required in order to meet the hydrological
goal, a sensitivity analysis has to be done by which the amount of satellite data to
be used can be optimized.
18.3 Application
In order to show, how the approach described in Sect. 18.2 functions in practice an
example will be presented.
Due to the fact that the approach discussed here is mainly meant for planning of
water management systems in countries of the developing world, it seems appropriate to give an example from the tropics. On the basis of an existing cooperation
between the Institute of Hydrology, Water Management and Environmental Techniques of the Ruhr-University Bochum and the Water Resources Research Unit,
CSIR, in Ghana, West Africa, the Tano river basin in Ghana was chosen.
IS.3.1 Study area and data used
The Tano river basin comprises a catchment area of about 16.000 km 2 , in which
daily records from 23 raingauges for the period of 1983-1984 are available. The
raingauge density is 1 gauge per 700 km 2 and their distribution over the catchment
is reasonably uniform. Additionally measured monthly runoff values and monthly
rainfall for the periods from 1969 - 1972, 1975 - 1976 and 0711984 - 0411985 are
also available. The observed daily rainfall data are accumulated in monthly values,
since for planning purposes of water management systems monthly data are usually adequate. The required monthly area precipitation is computed from the available point measurements with the aid of the reciprocal distance weighting method.
In West Africa, where the test catchment is located, rainfall intensity and distribution in space is dependent on the migration of the ITDZ (Inter Tropical Discontinuity Zone). The ITDZ is the front where two air masses of different origin and
characteristics converge (Tropical Continental Air Mass and Tropical Maritime
Air Mass). The migration of the ITDZ gives rise to two well-defined seasons (wet
and dry). The months July and August are dry although the ITDZ is farthest north
(wet season) which means that the atmospheric water vapour is high. This situation
is defmed as a climatic anomaly over West Africa. Especially for the Tano river
basin two main seasons are defined, namely the wet season in which the whole
catchment area under consideration is influenced only by maritime air masses
excluding the months July and August (short dry season) and the dry or relatively
dry season in which the catchment area is influenced mostly by continental air
masses (Ojo, 1977). Figure 18.5 shows the location of the catchment in a semi-arid
area in Ghana, West Africa.